This invention relates generally to apparatus for converting circular motion to radial motion, particularly for applications in the manufacture of vehicle tires.
In the manufacture of vehicle tires, there are several manufacturing operations which include a variable diameter mandrel, such as the drum employed in the lay-up of a tire carcass, bead locking mechanisms, shaping drums, and transfer rings. In each such mandrel, it is required that the mandrel include means for adjusting the diameter of the mandrel, such as for establishing the desired diameter of the tire carcass, for radial collapse of the drum to facilitate removal of a formed or partially formed tire carcass from a mandrel, for radial movement of grasping and supporting shoes of a transfer ring, etc.
By way of example, in the manufacture of vehicle tires, one process operation includes positioning of a green tire carcass on a shaping drum whereupon the carcass is inflated to a generally desired toroidal shape. The green tire carcass normally is of a generally hollow cylindrical geometry having a non-extensible bead ring secured internally of each of the opposite ends of the carcass. The shaping drum of the prior art includes first and second generally cylindrical mandrels which are disposed on opposite sides of a centerplane oriented perpendicular to the longitudinal centerline of the drum. This longitudinal centerline also defines the rotational axis of the drum. The mandrels of a shaping drum are designed to engage the bead ring-containing opposite ends of the carcass and thereby hold the carcass centered on the drum relative to the centerplane and concentric with respect to the rotational axis of the drum.
Commonly, each of the two mandrels of a shaping drum is of the radially expansible type, that is, each mandrel comprises a plurality of segments which are disposed radially about the rotational axis of the drum and which collectively define generally the outer circumference of an annular receiver for one of the bead rings of the carcass. The segments of each mandrel are radially moveable relative to the rotational axis of the drum for locking the bead rings of the carcass to the drum and are laterally movable to permit initial selection of the spacing between the bead rings as the carcass. and adjustment of their lateral spacing as the carcass is radially expanded to define a green tire.
For proper functioning of the shaping drum and true rotational dimensioning of the carcass into a vehicle tire, it is important that the carcass initially be positioned precisely centrally of the shaping drum both radially of the drum and laterally of the centerplane of the drum so that upon inflation of the carcass toward a toroidal geometry, all parts of the carcass move or expand uniformly with respect to one another, thereby ensuring uniformity of symmetry of the expanded carcass, as well as uniformity of distribution of the material of construction of the carcass, and ultimately, uniformity of the radial and lateral dimensions and material distribution of the finished tire.
A typical green tire carcass for a truck tire, for example, will weigh 35-50 pounds or more and is relatively flimsy and difficult to manipulate. Accordingly, loading of the carcass onto a shaping drum is difficult in several aspects. For example, manually placing the carcass onto the drum from one end of the drum, that is xe2x80x9cthreadingxe2x80x9d of the carcass initially onto one end of the drum and further moving the carcass toward the lateral centerplane of the drum is difficult in that the carcass tends to bend, twist, collapse and/or sag due to gravity, from its open cylindrical geometry when lifted by an operator or a mechanical transfer device. After the carcass has been initially threaded onto the drum, there remains the problem of completing the centering the carcass relative to the lateral centerplane of the drum so that the bead rings are disposed on opposite sides of, and equidistantly from the centerplane of the drum and equidistant radially about the rotational axis of the drum. These and other positioning efforts are frustrated by the tendency of the carcass to xe2x80x9csagxe2x80x9d under the effects of gravity thereby impeding the radial centering of the carcass relative to the longitudinal centerline of the drum before, or as, the bead rings become locked to the mandrels of the drum. Failure to center the carcass both radially and longitudinally of the shaping drum can result in non-uniform distribution of the material of the carcass, hence of the finished tire, with the result that the finished tire is unacceptably xe2x80x9cout of roundxe2x80x9d and must be scrapped.
In the prior art, there exist numerous mechanisms for adjusting the diameter of a mandrel, such as a drum or transfer ring employed in the manufacture of vehicle tires. These mechanisms, generally, are bulky and therefore in some embodiments they occupy a considerable portion of the interior volume of a mandrel and thereby limit particularly the minimum diameter of a given mandrel, as well as limiting the maximum diameter of the drum. In other embodiments, the expansion mechanism is disposed intermediate laterally adjacent components of the mandrel (drum, etc.) and present obstacles to various relative movements of various components of the mandrel. Moreover, such prior art systems are costly to manufacture and to maintain, in part due to their complexity and/or to their location within or on the mandrel.
In accordance with one aspect of the present invention there is provided apparatus and a method for converting circular motion to radial motion. The present invention is particularly useful in variable diameter mandrels (drums and/or transfer rings) employed in the manufacture of vehicle tires.
In one embodiment of the apparatus of the present invention, a mandrel is provided which includes a generally circular tubular housing. Internally of the tubular housing there are disposed a plurality of partitions which are anchored at spaced apart locations about the toroidal dimension of the housing and which define fixed fluid-tight seals across the cross-sectional area of the housing. Adjacent ones of the partitions define therebetween a fluid-tight chamber whose outer wall is defined by the housing wall. Within the chamber defined between adjacent ones of the partitions, there is provided a piston member which is slidable between a first position in which one end of the piston member is adjacent a first one of its adjacent partitions and the opposite end of the piston is spaced apart from a second one of the adjacent partitions, and a second position in which the opposite end of the piston member is adjacent the second one of its adjacent partitions and the first end of the piston member is spaced apart from the first adjacent partition. In one embodiment of the apparatus, each piston member has operatively associated therewith the proximal end of a linkage adapted to convert circular motion of its piston member within the housing into radial movement of the distal end of the linkage. As desired, appropriate working elements, or the like, may be mounted on the distal ends of a plurality of linkages. In one example, the working elements may be segments which, collectively, at least partially define a circumferential dimension (hence diameter) of the mandrel. Pressurized fluid, air for example, may be employed to power the circular, preferably simultaneous, movement of the piston members disposed within the toroidal housing, hence simultaneous radial movement of the accompanying distal ends of the linkages, hence adjustment of the effective diameter of the mandrel. In a further embodiment, selected ones of the piston members, hence their associated linkages, may be moved in a clockwise direction while simultaneously, others of the piston members disposed within the housing may be moved in a counter clockwise direction, thereby causing the distal ends of selected ones of the linkages to move toward a minimum diameter while others of the distal ends of others of the linkages move toward a maximum diameter.